Resistance heating apparatus for elongated workpieces of varied lengths

ABSTRACT

An apparatus for resistance heating elongated workpieces having random lengths varying between defined limits wherein during heating a single workpiece is transversely gripped between two spaced apart pairs of resistance heating contacts. The apparatus includes means for selectively moving each pair of contacts transversely toward and away from each other to provide for efficient heating of workpieces having various random lengths. Associated with each pair of contacts are means for automatically determining the proper amount of transverse movement for each workpiece to be heated and means for permitting the pairs of contacts to move further transversely away from each other during heating to compensate for longitudinal workpiece expansion.

United States Patent 1191 Day RESISTANCE HEATING APPARATUS FOR ELONGATED WORKPIECES 0F VARIED LENGTHS [75] Inventor: Paul L. Day, Middleburg Heights,

Ohio

[73] Assignee: Park-Ohio Industries, lnc.,Cleveland, Ohio [22] Filed: Sept. 20, 1971 [21] Appl. No.: 181,880

[56] References Cited UNITED STATES PATENTS 5/1930 MacDonald etal. .1219/156 12/1968 12112010 et 31...... 219/156 [111 3,743,778 14 1 July 3, 1973 Primary Examiner-R. F. Staubly Assistant Examiner-L. A. Schutzman Attorney-Meyer, Tilberry & Body ABSTRACT An apparatus for resistance heating elongated workpieces having random lengths varying between defined limits wherein during heating a single workpiece is transversely gripped between two spaced apart pairs of resistance heating contacts. The apparatus includes means for selectively moving each pair of contacts transversely toward and away from each other to provide for efficient heating of workpieces having various random lengths. Associated with each pair of contacts are means for automatically determining the proper amount of transverse movement for each workpiece to be heated and means for permitting the pairs of contacts to move further transversely away from each other during heating to compensate for longitudinal workpiece expansion.

12 Claims, 11 Drawing Figures Patented July 3, 1973 3,743,778

4 Sheets-Sheet l INVENTOR. PAUL L. DAY

BY Mega, 7M 8 Body ATTORNEYS Patented July 3, 1973 4 Sheets-Sheet 2 ATTORNEYS Patented July 3, 1973 3,743,778

4 Sheets-Sheet 3 80 82 INVENTOR.

PAUL L. DAY

' BY Ma 744%, g 80d,

ATTORNEYS Patented July 3, 1973 4 Sheets-Sheet 4 FIG. 9

INVENTOR. PAUL L. DAY

FIG. I0

FIG. II

BY Meyajllmy 8 ATTORNEYS 1 RESISTANCE HEATING APPARATUS FOR ELONGATED WORKPIECES F VARIED LENGTHS This application pertains to the art of resistance heating and more particularly to a resistance heating apparatus for elongated workpieces.

The invention is particularly applicable for use in resistance heating elongated generally cylindrical workpieces having substantially the same diameter and random lengths, such as for example, steel shafts, and will be described with particular reference thereto; however, it will be appreciated that the invention has broader applications and may be used in other instances where it is desired to employ resistance type heating to elongated workpieces having any cross sectional configuration and random lengths.

l-leretofore, resistance heating apparatus which have been employed for resistance heating these elongated workpieces have been generally comprised of two pairs of spaced apart resistance heating contacts. Each pair included two opposed contact portions wherein at least one portion of each pair was movable toward and away from its associated portion. In operation, a workpiece was first placed between the contact pairs in a desired spaced relationship therewith and the movable portions of each contact pair were then directed toward their associated portions so as to clamp the workpiece there- 'between. A heating current was then applied to the workpiece through the heating contactsby means of an outside current supply source. Following heating, the movable portions were retracted 'to allow removal of the heated workpiece and insertion of a new unheated workpiece.

In resistance heating elongated workpieces, it is often desirous to heat elongated workpieces having random lengths in order to fulfill particular production requirements. Oftentimes, the heating criteria for these random lengths is the same so that a single universal type heating apparatus could be employed instead of heating only one length of workpiece at a time and readjusting the heating apparatus for each batch of workpieces of different lengths. The necessity for this adjustment will be appreciated when it is understood that the most efficient resistance heating is attained when the workpiece to be heated is clamped adjacent to the ends.

However, in the above type or previously used heating apparatus, the contact pairs were spaced apart in sucha manner that the relative transverse distance therebetween could only be changed by making time consuming and difficult adjustments to the apparatus. For this reason, it was only possible, from a practical standpoint, to heat workpieces of a single length at a time. If other lengths were desired to be heated, the apparatus would be adjusted to accommodate efficient heating as required. Obviously, this practical necessity caused a substantial amount of apparatus idle time and did not permit a flexible heating operation when a plurality of lengths of workpieces were involved.

The present invention contemplates a new and improved apparatus which overcomes all of the above referred problems and other generally associated therewith and provides a new apparatus for resistance heating elongated workpieces which provides efficient heating, permits high production outputs to be attained, and permits efficient resistance heating of comingled workpieces of random lengths.

In accordance with the present invention, there is provided a resistance heating apparatus for heating an elongated workpiece selected from a plurality of workpieces having random lengths. The apparatus includes first and second pairs of spaced apart workpiece contacts and first means for moving the contacts of the first and second pairs between a first opened condition and a second workpiece clamping condition with the workpiece extending generally transversely therebetween. Means are provided for selectively transversely forcing the first pair of contacts relative to the second pair of contacts between a first spaced normal position and a second spaced heating position while the contacts of the first pair are in the first condition. The second position is determined by the length of the workpiece and means for determining this second position at least by the time the first pair of contacts is moved from the first to the second position are provided. The apparatus further includes means for causing the first means to move the contacts of thefirst pair of contacts into the second condition after the first of contacts is in the second position and means for supplying electrical energy to the pairs of contacts for resistance heating the workpieces when the pairs of contacts are in the second condition.

In accordance with a more limited aspect of the present invention, means are provided for selectively transversely forcingthe'second pair of contacts relative to the first pair of contacts between a third spaced normal positionand a fourth spaced heating position while the contacts of thesecond'pair of contacts are in the first condition. Means for determining the fourth position and means for causing the first means to move the contacts of the second pair of contacts into the second condition after the second pair of contacts are in the fourth positionare also provided.

In accordance with another limited aspect of the present invention, there is provided an improved resistance heating apparatus for elongated workpieces which permits workpieces having random lengths to be efficiently heated without the need for time consuming apparatus adjustments having to be made.

The principal object of the present invention is the provision'of a resistance heating apparatus for successively heating elongated workpieces of random lengths.

Another object of the present invention is the provision of a resistance heating apparatus for heating elongated workpieces which is more versatile than prior apparatus.

Yet another object of the present invention is the provision of a resistance heating apparatus for elongated workpieces in which the contacts are automatically adjustable to accommodate workpieces of random lengths.

Still another object of the present invention is the provision of a resistance heating apparatus for heating elongated workpieces which permits contact move ment in order to compensate for longitudinal expansion of a workpiece during heating.

Another object of the present invention is the provision of an improved contact mounting for resistance heating apparatus for elongated workpieces which permits workpieces of random lengths to be efficiently heated.

The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein:

FIG. 1 is a side view of an apparatus which includes the subject invention;

FIG. 2 is a cross sectional view taken along lines 2--2 of FIG. 1;

FIG. 3 is a cross sectional view taken along lines 3-3 of FIG. 2;

' FIG. 4 is a cross sectional view taken along lines 4-4 of FIG. 2;

FIG. 5 is a cross sectional view taken along lines 5-5 of FIG. 2; and,

FIGS. 6-11 are schematic diagrams showing the operation of the subject apparatus.

Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiment of the invention only and not for purposes of limiting same, the FIGURES show an apparatus having a resistance heating portion A, workpiece supply area B, workpiece feeder system C, workpiece removal system D, electrical supply area E and apparatus framework F. v

Specifically, and with reference to FIGS. 1, 2 and 4 and resistance heating portion A, it will be seen that it includes a pair of spaced apart contact arm assemblies 10,12 received on an elongated mounted shaft 13 supported by apparatus framework F in any convenient manner. It is to be appreciated that assemblies 10,12 are identical to and oppositely disposed from each other so that description will hereinafter only be made with reference to assembly 10, it being understood that assembly 12 is identical thereto unless otherwise specifically noted. Assembly includes a contact arm assembly hub 14 which comprises that portion of the assembly which is received over mounting shaft 13. The hub is received thereon in a sliding relationship so that assembly 10 may be moved longitudinally therealong in either direction. Pivotally mounted to the hub by convenient means are contact arms 16,18 which form a scissors-like assembly. A fluid cylinder is operatively disposed between the contact arms at one end thereof to drive the other ends of the arms between an open and closed relationship relative to each other. It will be appreciated that fluid cylinder 20 maybe comprised of any type of fluid cylinder, however, in the preferred embodiment, a pneumatic cylinder is employed and standard clevis mountings are used to affix the cylinder relative to the contact arms. Disposed immediately adjacent contact arms 16,18 on hub 14 are a pair of spur gears 22,24 respectively which intermesh with each other in order to assure unity of movement between arms 16,18. Use of these spur gears is known in the art.

With particular reference to FIG. 4, it will be seen that disposed on the opposite ends of contact arms 16,18 from fluid cylinder 20 are contact assemblies 26,28 respectively. This type of contact assembly is known and comprises insulators 30,32 spaced between the contact arms and copper contact blocks 34,36 respectively. The contact blocks include therein V- shaped workpiece receiving grooves 38,40 as is also known. Contact assemblies 26,28 may be made selfaligning by pivotally mounting them to arms 16,18 so they will at least pivot through a plane transverse to the plane of the associated contact arm assembly. The selfaligning feature permits compensation for workpiece run-out to assure the desired workpiece contact is obtained during heating.

Referring again to FIG. 2, it will be seen that disposed between contact arm assemblies 10,12 on mounting shaft 13 is an elongated power means mounting sleeve 50 which is permanently affixed in position to the shaft. Received on and mounted to the sleeve is a fluid cylinder 52 associated with assembly 10 and a fluid cylinder I The use of this movement will hereinafter be more fully described with reference to operation of the apparatus.

Also disposed on each contact arm assembly is a sensing assembly 60. As these assemblies are identical to each other, reference will hereinafter be made only to the sensing assembly disposed on contact arm assembly 10, it being understood that the other sensing assembly is identical thereto unless otherwise specifically noted. Assembly 60 is best seen in FIGS. 2, 3 and 5 and includes a mounting block 62 conveniently mounted to hub 14. Extending through the mounting block is an elongated sensing shaft 64 disposed to be generally parallel to mounting shaft 13 and coaxial with a workpiece in the heating position as will be hereinafter described. A collar 66 is received adjacent one end of the sensing shaft and a second collar 68 is received adjacent the other end of the sensing shaft. Between mounting block 62 and collar 66 is disposed a coil spring 70 so as to continuously bias the sensing shaft inwardly. A generally L-shaped mounting bracket 78 is received on the bottom of mounting block 62 and has located thereon a pair of contact switches 80,82. Although the switches may be comprised of any type of switch in the preferred embodiment of the invention, a micro-type switch is employed which includes switch heads 81,83 respectively for activation thereof in a conventional manner. These switches are interconnected with the operational circuitry for cylinders 52,54 as will hereinafter be more fully explained with reference to operation of the apparatus. With particular reference to FIG. 5, mounting block 62 is received relative to hub 14 by a dove-tail mounting generally designated 84 so as to permit relative movement between the two. A fluid cylinder 86 is also mounted to hub 14 by any convenient means and includes cylinder rod 88. This cylinder rod is connected to mounting block 62 in order that sensing assembly 60 may be moved relative to hub 14 in a direction generally parallel to mounting shaft 13 as will hereinafter be described. I

workpiece supply area B is comprised of a workpiece magazine of any conventional type known for handling elongated steel shafts. In the preferred embodiment of the invention, the magazine includes a loading end 102 and a feeding end 104 disposed therebelow for gravity-type feeding. As seen in FIG. 1, a plurality of cylindrical steel shafts 106 are placed in the magazine in a side-by-side relationship. It should be here noted that the workpieces may be of random or of varying lengths but should be of substantially the same diameter. Spaced immediately adjacent feeding end 104 is a shaft receiving head 108 which includes a generally U-shaped channel 110 therein adapted for receiving an elongated shaft 106. A fluid cylinder 112 is disposed therebelow and includes a cylinder rod 114 connected with the head so that in the retracted position of the cylinder the head is immediately adjacent feeding end 104 to receive workpiece 106 and in the extended position the head is disposed adjacent resistance heating portion A. A head extension 116 is provided to extend between head 108 and cylinder 112 and acts to prevent workpieces 106 from leaving the magazine when the head is moved to the extended position.

The actual feeding and locating of the workpieces is accomplished by a workpiece feeding unit 120. The unit includes a workpiece receiving head 122 having therein three generally U-shaped support areas 124,126 and 128 as are best shown in FIG. 2. A fluidcylinder 130 which has a cylinder rod 132 interconnected with head 122 forces the head toward resistance heating area A when cylinder 130 is expanded. During its travel, support areas 124,126 and 128 lift the workpiece from head 108 and carry it into the proximity of the contact assemblies. Following heating, these support areas carry the heated workpieces to workpiece removal system D as will hereinafter be more fully described.

Workpiece removal system D is comprised of a conventional chain conveyor 140, one side of which is shown in FIG. 1. The conveyor includes a pair of spaced apart sprockets 142,144 mounted on shafts 146,148 respectively and having a chain 150 extending continuously therearound. One of these sprockets is driven by conventional means (not shown) to effect movement of workpieces 106 in the direction a as shown in that FIGURE. It will be understood that the other side of the chain conveyor is identical to that hereinabove described. A chute-like area 152 is disposed immediately adjacent the rear end of the chain conveyor to guide workpieces 106 from the conveyor to a second conveyor or roller apparatus 154 for movement of the workpieces to storage or subsequent operations.

Electrical supply area B is conventional and is therefore not shown in detail. It supplies 60 cycle electrical current through the necessary electrical cables to the contact assemblies. At the same time, and also as is conventional, coolant fluid is supplied through coolant supply lines (not shown), also conventional, to maintain the contact assemblies below their melting temper- I atures.

Apparatus framework F includes a plurality of tubular vertical frame members, tubular horizontal frame members and tubular angled frame members..lt is to be understood that the frame is designed so as to mount the individual component assemblies as hereinabove previously described in the required relative positions. Further, it is possible to include a sheet metal housing around this framework so as to protect the components from destructive elements oftentimes found in industrial environments, to protect workmen coming into contact with the apparatus and to present a single unit package. As the framework itself does not form a part of the present invention, it is not more fully described.

In describing the operation of the subject invention, reference will be made to one workpiece 106 and to FIGS. 6-11. Prior to heating any one workpiece, cylinders 20 are moved to a retracted position so that contact assemblies 26,28 will be spaced apart from each other in a first condition. Similarly, cylinders 52,54 are moved to their expanded positions so that contact arm assemblies 10,12 are moved along mounting shafts 13 to their furtherrnost spaced apart positions. Cylinders 86 are also moved to their expanded positions so that sensing assemblies 60 are moved inwardly toward each other.

With the resistance heating portion A in this condition (FIG. 6), a single workpiece 106 is gravity fed from feeding end 104 of magazine into channel 110 of head 108 and then lifted by head 108 during extension of fluid cylinder 112 to a position adjacent resistance heating portion A. Head extension 116 functions to retain the remainder of the shafts in the magazine from exiting at feeding end 104 when head 108 is in this raised position. With the workpiece adjacent the resistance heating portion, and with reference to FIG.

7, shaft receiving head 122 is moved toward the resistance heating portion by cylinder 130. Along this movement, the shaft receiving head picks up workpiece 106 from shaft receiving head 108 and moves it into close proximity with the contact areas. Following this pick up, cylinder 1 12 may be retracted so that head 108 will be again moved to a position adjacent feeding end 104 for the receipt of a second workpiece 106 in channel 110. FIG. 8 is identical to the view of FIG. 7 except that it is taken in another direction to more adequately show the proximity of the workpiece to the contact areas and the location of support areas 124,126 and 128 to the workpiece. It should be here noted that contact arm assemblies 10,12 are spaced apart a distance greater than the overall length of the workpiece to be heated. It should be further noted that sensing shafts 64 extend inwardly through and beyond the inside edges of the open contact areas.

At this point, and with reference to FIG. 9, cylinders 52,54 are energized to retract and thereby simultaneously draw contact arm assemblies 10,12 respectively toward each other in the direction b shown in that FIGURE. As the contact arm assemblies approach the ends of the workpiece, sensing shafts 64 engage the ends of the workpiece and are forced outwardly in direction C overcoming the inwardly biasing pressure exerted by coil springs 70. During this movement, collars 68 energize switches 80 by trippling switch heads 81. These switches are interconnected with the control circuitry for cylinders 52,54 so that upon their energization, the inward movement of the contact arm assemblies in direction b is slowed. Generally,.this slowing movement occurs when the contact areas are immedi ately adjacent the end points of workpiece 106.

With reference to FIG. 10, cylinders 52,54 continue to draw contact arm assemblies 10,12 toward each other so that sensing shafts 64 are directed further outwardly in directions C until collars 68 trip switch heads 83 of contact switches 82. Switches 82, like switches 80, are interconnected with the control circuitry for cylinders 52,54 so that when they are energized, the inward movement or retraction of the cylinders is immediately stopped. In this position, contact arm assemblies are in the proper position so that the contacts will grip the workpiece immediately adjacent the end points thereof to provide the desired resistance heating contact. Cylinders 20 may then be energized to the extended position so that the workpiece will be gripped and clamped at the end points by contact assemblies 26,28. When switches 82 have been energized, there is no further need for the sensing assemblies so that fluid cylinders 86 are energized to retract (FIG. 11) and thereby draw the assemblies outwardly in directions d away from association with the workpiece and contact arm assemblies. workpiece feeding unit 120, and in particular, suppport areas 124, 126 and 128 hold the workpiece in the desired elevated position so that it is gripped in the V-shaped workpiece receiving grooves 38,40 of contact block 34,36 respectively. Once the workpiece is gripped between the contact assemblies,

,all fluid pressure on cylinders 52,54 is released andthe electrical supply area B energized so as to provide current to the contact blocks with resultant current flow through the workpiece between the contact arm assemblies to thus effect the desired resistance heating. As is known, elongated workpieces experience longitudinal expansion during heating and the pressure release from fluid cylinders 52,54 permits contact arm assemblies 10,12 to freely move away from each other along mounting shaft 13 to compensate for longitudinal expansion as it occurs. it should here be noted that during heating, shaft receiving head 122 is retained in its supporting position to assist in preventing bowing of the workpiece.

Temperature sensors 160,162 (FIGS. 1 and 2) detect when workpiece 106 has been heated to a predetermined desired temperature and effect shut off of the electrical supply area. At this shut off, cylinders are moved to the retracted position so that the contact blocks of each contact assembly once again become spaced apart in order that the workpiece may be removed therefrom. As the support areas 124,126 and 128 of shaft receiving head 122 are generally U-shaped in cross sectional configuration, they act as strippers for stripping the workpiece from contact with the contact blocks. Once the contact assemblies have been opened, cylinder 52,54 and 86 may be again moved to their initial position as described with reference to FIG. 6 in anticipation of another workpiece heating cycle. Cylinder 130 may be retracted to withdraw the workpiece which has just been heated from association with the resistance heating portion A. As shown in FIG. 6, as cylinder 130 is completely retracted, the heated workpiece is laid on chain conveyor 140 for transport to conveyor or rolls 154. As cylinder 130 is being retracted, cylinder 112 may again be extended carrying another workpiece to a position adjacent the resistance heating portion A and the entire process as hereinabove described may be repeated for each workpiece to be heated.

As can be seen, the operation of the apparatus hereinabove described provides for the heating of workpieces having varying or random lengths as the transverse distance between contact arm assembly 10,12 are reset for each workpiece as it is located in proximity with the contact assemblies.

The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon the reading and understanding of this specification. It is my intention to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalence thereof.

Having thus described my invention, I now claim:

, l. A resistance heating apparatus for heating an elongated workpiece having longitudinal axis and which has been selected from a plurality of workpieces having random lengths, said apparatus comprising:

first and second pairs of spaced apart workpiece contacts, the contacts comprising each of said pairs being mounted for movement relative to each other between a first opened condition and a second heating condition with said workpiece clamped therebetween;

first means for selectively moving the contacts of said first and second pairs of contacts between said first opened condition and said second heating condition;

power means for selectively moving at least said first pair of contacts longitudinally of said workpiece toward and awayfrom said second pair of contacts between a first normal position and a second heating condition while at least said first pair of contacts is in said opened first condition;

means for automatically determining said second position in response to the length of said workpiece before at least said first pair of contacts is moved from said first opened condition to said second heating condition; and,

means for supplying electrical energy to said pairs of contacts for resistance heating said workpiece when said first pair of contacts is in said second position with the contacts of both said first and second pairs'of contacts in said second condition.

2. The apparatus as defined in claim 1 wherein said power means includes means for allowing said first pair of contacts to be spaced apart from said second pair of contacts longitudinally of said workpiece a distance greater than the length of said workpiece when said first pair of contacts is in said first position.

3. The apparatus as defined in claim 2 wherein said first and second pairs of contacts are spaced generally equidistantly from the center of said workpiece along the length thereof when said first pair of contacts is in said second position.

4. The apparatus as defined in claim 1 further including power means for selectively moving said second pair of contacts generally longitudinally of said workpiece toward and away from said first pair of contacts between a third normal position and a fourth heating position while at least said second pair of contacts is in said first condition; and,

means for automatically determining said fourth position in response to the length of said workpiece before said second pair contacts is moved from said first condition to said second condition.

5. The apparatus as defined in claim 4 wherein said second position determining means and said fourth position determining means comprise sensing means disposed on each of said first and second pairs of contacts for sensing the relative positions of said contacts to said workpiece during movement of said first pair of contacts from said first toward said second position and said second pair of contacts from said third toward said fourth position longitudinally of said workpiece.

6. The apparatus as defined in claim 5 wherein said sensing means are operably interconnected with said moving means for both of said first and second pairs of contacts for automatically de-energizing each of said moving means as said sensing means automatically sense said second and fourth positions when said first pair of contacts is moved from said first position toward said second position and said second pair of contacts is moved from said third position toward said fourth position.

7. The apparatus as defined in claim 6 further including means for selectively releasing the moving connections between the moving means and said first and second pairs of contacts when said first pair of contacts is in said second condition at said second position and when said second pair of contacts is in said second condition at said fourth position.

8. The apparatus as defined in claim wherein the distance between said first and third positions longitudinally of said workpiece is greater than the length of said workpiece, said sensing means disposed on said first pair of contacts engaging one end of said workpiece as said first pair of contacts is moved from said first toward said second position with said sensing means disposed on said second pair of contacts engaging the other end of said workpiece as said second pair of contacts is moved from said third toward said fourth position.

9. In a resistance heating apparatus for heating an elongated workpiece having an axis wherein said apparatus includes first and second pairs of heating contacts spaced axially of said workpiece and each of said pairs of contacts being movable between a first opened condition and a second workpiece clamping condition with a workpiece extending therebetween and means for supplying electrical energy to said pairs of contacts when said pairs of contacts are in said second condition, the improvement comprising: I

power means for selectively moving said first pair of contacts toward and away from said second pair of contacts longitudinally ofsaid workpiece between a first normal position and a second heating position while at least the contacts of said first pair of contacts are in said first condition;

means for automatically determining said second position in response to the length of said workpiece before at least said first pair of contacts is moved from said first condition to said second condition; and, means for shifting said first pair of contacts into said second condition after said determining means determines that said first pair of contacts is in said second position.

10. The improvement as defined in claim 9 further including power means for selectively moving said second pair of contacts toward and away from said first pair of contacts longitudinally of said workpiece between a third normal position and a fourth heating position; and, means for automatically determining said fourth position in response to the length of said workpiece before said second pair of contacts is moved from said first condition to said second condition.

11. The improvement as defined in claim 10 wherein the distance between said first pair of contacts first position and said second pair of contacts third'position longitudinal of said workpiece is greater than the length of said workpiece.

12. The improvement as defined in claim 10 furthe including means for automatically de-energizing both of said moving means when said determining means determine said second and fourth position for said first and second pairs of contacts respectively and means for releasing the moving connections between the moving means for both said first and second pairs of contacts when said first pair of contacts is in said second condition at said second position and when said second pair of contacts is in said second condition at said fourth position. 

1. A resistance heating apparatus for heating an elongated workpiece having a longitudinal axis and which has been selected from a plurality of workpieces having random lengths, said apparatus comprising: first and second pairs of spaced apart workpiece contacts, the contacts comprising each of said pairs being mounted for movement relative to each other between a first opened condition and a second heating condition with said workpiece clamped therebetween; first means for selectively moving the contacts of said first and second pairs of contacts between said first opened condition and said second heating condition; power means for selectively moving at least said first pair of contacts longitudinally of said workpiece toward and away from said second pair of contacts between a first normal position and a second heating condition while at least said first pair of contacts is in said opened first condition; means for automatically determining said second position in response to the length of said workpiece before at least said first pair of contacts is moved from said first opened condition to said second heating condition; and, means for supplying electrical energy to said pairs of contacts for resistance heating said workpiece when said first pair of contacts is in said second position with the contacts of both said first and second pairs of contacts in said second condition.
 2. The apparatus as defined in claim 1 wherein said power means includes means for allowing said first pair of contacts to be spaced apart from said second pair of contacts longitudinally of said workpiece a distance greater than the length of said workpiece when said first pair of contacts is in said first position.
 3. The apparatus as defined in claim 2 wherein said first and second pairs of contacts are spaced generally equidistantly from the center of said workpiece along the length thereof when said first pair of contacts is in said second position.
 4. The apparatus as defined in claim 1 further including power means for selectively moving said second pair of contacts generally longitudinally of said workpiece toward and away from said first pair of contacts between a third normal position and a fourth heating position while at least said second pair of contacts is in said first condition; and, means for automatically determining said fourth position in response to the length of said workpiece before said second pair contacts is moved from said first condition to said second condition.
 5. The apparatus as defined in claim 4 wherein said second position determining means and said fourth position determining means comprise sensing means disposed on each of said first and second pairs of contacts for sensing the relative positions of said contacts to said workpiece during movement of said first pair of contacts from said first toward said second position And said second pair of contacts from said third toward said fourth position longitudinally of said workpiece.
 6. The apparatus as defined in claim 5 wherein said sensing means are operably interconnected with said moving means for both of said first and second pairs of contacts for automatically de-energizing each of said moving means as said sensing means automatically sense said second and fourth positions when said first pair of contacts is moved from said first position toward said second position and said second pair of contacts is moved from said third position toward said fourth position.
 7. The apparatus as defined in claim 6 further including means for selectively releasing the moving connections between the moving means and said first and second pairs of contacts when said first pair of contacts is in said second condition at said second position and when said second pair of contacts is in said second condition at said fourth position.
 8. The apparatus as defined in claim 5 wherein the distance between said first and third positions longitudinally of said workpiece is greater than the length of said workpiece, said sensing means disposed on said first pair of contacts engaging one end of said workpiece as said first pair of contacts is moved from said first toward said second position with said sensing means disposed on said second pair of contacts engaging the other end of said workpiece as said second pair of contacts is moved from said third toward said fourth position.
 9. In a resistance heating apparatus for heating an elongated workpiece having an axis wherein said apparatus includes first and second pairs of heating contacts spaced axially of said workpiece and each of said pairs of contacts being movable between a first opened condition and a second workpiece clamping condition with a workpiece extending therebetween and means for supplying electrical energy to said pairs of contacts when said pairs of contacts are in said second condition, the improvement comprising: power means for selectively moving said first pair of contacts toward and away from said second pair of contacts longitudinally of said workpiece between a first normal position and a second heating position while at least the contacts of said first pair of contacts are in said first condition; means for automatically determining said second position in response to the length of said workpiece before at least said first pair of contacts is moved from said first condition to said second condition; and, means for shifting said first pair of contacts into said second condition after said determining means determines that said first pair of contacts is in said second position.
 10. The improvement as defined in claim 9 further including power means for selectively moving said second pair of contacts toward and away from said first pair of contacts longitudinally of said workpiece between a third normal position and a fourth heating position; and, means for automatically determining said fourth position in response to the length of said workpiece before said second pair of contacts is moved from said first condition to said second condition.
 11. The improvement as defined in claim 10 wherein the distance between said first pair of contacts first position and said second pair of contacts third position longitudinal of said workpiece is greater than the length of said workpiece.
 12. The improvement as defined in claim 10 further including means for automatically de-energizing both of said moving means when said determining means determine said second and fourth position for said first and second pairs of contacts respectively and means for releasing the moving connections between the moving means for both said first and second pairs of contacts when said first pair of contacts is in said second condition at said second position and when said second pair of contacts is in said second condition at said fourth position. 